Quiet and perturbed ionospheric representation according to the electron content from GPS signals

Signals from Global Positioning System (GPS) satellites received at the surface of the Earth have passed through the terrestrial atmosphere and are therefore affected by refraction in the ionosphere. A large number of permanent dual frequencies GPS tracking stations have been built up in the last years and their data have proved to be suitable to study the ionosphere. The main goal of this paper is to assess the capability of these observations to continuously and routinely monitor the ionosphere at a global scale. The interest was focused on retrieving the coefficients of a spherical harmonics expansion that describe the global distribution of the vertical total electron content (VTEC) from the GPS signal. To test our results, we compare them with other GPS-derived results, with VTEC values computed with the International Reference Ionosphere (IRI-95) model, and with direct VTEC determinations provided by Topex-Poseidon satellite. A large set of global VTEC maps with a time resolution of 2 hours was used to describe the evolution of this ionospheric variable at quiet geomagnetic periods during the year 1997. The outstanding features of the VTEC during the 15 May 1997 geomagnetic storm have also been studied. The results show that our method is able to identify large-scale features and seasonal variations of the VTEC in quiet conditions, as well as its variations during a large geomagnetic storm.Facultad de Ciencias Astronómicas y Geofísica

Quiet and perturbed ionospheric representation according to the electron content from GPS signals

Signals from Global Positioning System (GPS) satellites received at the surface of the Earth have passed through the terrestrial atmosphere and are therefore affected by refraction in the ionosphere. A large number of permanent dual frequencies GPS tracking stations have been built up in the last years and their data have proved to be suitable to study the ionosphere. The main goal of this paper is to assess the capability of these observations to continuously and routinely monitor the ionosphere at a global scale. The interest was focused on retrieving the coefficients of a spherical harmonics expansion that describe the global distribution of the vertical total electron content (VTEC) from the GPS signal. To test our results, we compare them with other GPS-derived results, with VTEC values computed with the International Reference Ionosphere (IRI-95) model, and with direct VTEC determinations provided by Topex-Poseidon satellite. A large set of global VTEC maps with a time resolution of 2 hours was used to describe the evolution of this ionospheric variable at quiet geomagnetic periods during the year 1997. The outstanding features of the VTEC during the 15 May 1997 geomagnetic storm have also been studied. The results show that our method is able to identify large-scale features and seasonal variations of the VTEC in quiet conditions, as well as its variations during a large geomagnetic storm.Facultad de Ciencias Astronómicas y Geofísica

Ionospheric biases correction for coordinates derived from GPS single point positioning

Most GPS users employ low cost receivers. These receivers do not allow users to record the pseudorange that they observe, but the computed coordinates. This work presents an original and simple method to correct ionospheric biases introduced in GPS signals. The originality of this method is based on the fact that no pseudorange is needed to correct the biases, only the calculated coordinates are used. This distinguishes this method from other classic alternatives. This paper evaluates the efficiency of the method with the use of real data.Facultad de Ciencias Astronómicas y Geofísica

Posicionamiento diferencial mediante el uso de navegadores satelitales

El Sistema de Posicionamiento Global posee una gran variedad de usos, que van desde la determinación de movimientos tectónicos, que requiere exactitudes milimétricas, hasta la navegación recreativa, caso en que algunos metros de error en la posición resulta aceptable. Los costos del equipamiento están relacionados en forma directa con la exactitud requerida; como consecuencia de esto los trabajos geodésicos requieren receptores aproximadamente cien veces más caros que un navegador. Presentaremos aquí un trabajo que muestra como es posible mejorar en al menos un orden de magnitud las exactitudes de las coordenadas que usualmente provee un navegador, utilizando técnicas clásicas de posicionamiento diferencial. Se examinan diferentes casos donde se muestra como es posible obtener exactitudes entre pocos decímetros y el metro. Los casos analizados involucran distintas longitudes de base y distintos lapsos de tiempo de observación. De esta manera se estima el valor óptimo de tiempo de observación en función de la distancia, así como el límite de la exactitud que se puede alcanzar en cada caso. Finalmente se muestra que, si bien la alternativa que se presenta no puede reemplazar a los receptores geodésicos para trabajos de alta precisión, puede sin embargo ser muy útil cuando se requieran exactitudes decimétricas; siendo su atractivo principal el bajo costo del instrumental requerido.The Global Positioning System is used for a great variety of applications, from crustal movement estimation where sub-centimeter accuracy is required, to recreational navigation where errors of several meters are acceptable. The equipment cost is directly related to the required accuracy; hence receivers for geodetic applications are approximately one hundred times more expensive than those for navigation purposes. In this paper we show the possibility to improve the accuracy provided by a hand-held GPS receiver by using the well-known differential positioning technique. We analyze the results of a series of experiments involving different baseline lengths as well as several measurement intervals. This allows for the estimation of an optimum relationship between measurement interval and baseline length. The obtained accuracies range from few decimeters to one meter. We finally show that, though the presented alternative cannot replace the geodetic receivers for high precision requirements, it can nonetheless be quite useful when decimeter-level accuracies are required. Its main attraction is the low cost of the equipment needed.Material digitalizado en SEDICI gracias a la colaboración de la Facultad de Ciencias Astronómicas y Geofísicas (UNLP).Asociación Argentina de Geofísicos y Geodesta

SiGOG: simulated GPS observation generator

For many applications, access to unbiased or error-controlled global positioning system (GPS) observations can be very useful. This paper is devoted to the description of simulated GPS observations generator (SiGOG), a software that simulates GPS observations. It presents the results of tests of SiGOG accuracy using GPS processing software, and demonstrates its successful performance as a differential GPS (DGPS) correction provider.Facultad de Ciencias Astronómicas y Geofísica

Quiet and perturbed ionospheric representation according to the electron content from GPS signals

Signals from Global Positioning System (GPS) satellites received at the surface of the Earth have passed through the terrestrial atmosphere and are therefore affected by refraction in the ionosphere. A large number of permanent dual frequencies GPS tracking stations have been built up in the last years and their data have proved to be suitable to study the ionosphere. The main goal of this paper is to assess the capability of these observations to continuously and routinely monitor the ionosphere at a global scale. The interest was focused on retrieving the coefficients of a spherical harmonics expansion that describe the global distribution of the vertical total electron content (VTEC) from the GPS signal. To test our results, we compare them with other GPS-derived results, with VTEC values computed with the International Reference Ionosphere (IRI-95) model, and with direct VTEC determinations provided by Topex-Poseidon satellite. A large set of global VTEC maps with a time resolution of 2 hours was used to describe the evolution of this ionospheric variable at quiet geomagnetic periods during the year 1997. The outstanding features of the VTEC during the 15 May 1997 geomagnetic storm have also been studied. The results show that our method is able to identify large-scale features and seasonal variations of the VTEC in quiet conditions, as well as its variations during a large geomagnetic storm.Facultad de Ciencias Astronómicas y Geofísica

Ionospheric biases correction for coordinates derived from GPS single point positioning

Most GPS users employ low cost receivers. These receivers do not allow users to record the pseudorange that they observe, but the computed coordinates. This work presents an original and simple method to correct ionospheric biases introduced in GPS signals. The originality of this method is based on the fact that no pseudorange is needed to correct the biases, only the calculated coordinates are used. This distinguishes this method from other classic alternatives. This paper evaluates the efficiency of the method with the use of real data.Facultad de Ciencias Astronómicas y Geofísica

Impact of the extreme 2015-2016 ENOS event on the geometry of the earth surface in the equatorial region of South America

El fenómeno del Niño-Oscilación del Sur (ENOS) es un fenómeno oceánico-atmosférico que se origina en las aguas ecuatoriales del Océano Pacífico. Existen dos fases, la fase cálida o El Niño y la fase fría o La Niña, y se refieren respectivamente a un aumento o disminución considerable de la temperatura superficial del océano respecto de los valores normales. Una de las consecuencias de esta alteración es un impacto en el ciclo hidrológico de la región de Sudamérica y el Caribe. Dicho fenómeno provoca variaciones no periódicas tanto en los patrones de precipitaciones como en el almacenamiento de las masas hídricas, que se sitúan sobre la superficie o en regiones cercanas a ella. La consecuencia inmediata son cambios en la presión que dichas masas ejercen sobre la corteza terrestre, los que provocan movimientos geométricos de la corteza y cambios en las medidas de gravedad. El objetivo del presente trabajo es analizar el efecto geométrico que dicho fenómeno tiene sobre la posición de las estaciones GNSS que integran la red SIRGAS-CON. En este estudio se reconocen los períodos temporales en donde se produjeron fenómenos de El Niño o La Niña por medio del Índice Oceánico El Niño (ONI), y se analiza el impacto de los eventos más significativos, ocurridos en 2008-2012 y 2015-2016, sobre los patrones de precipitación y sobre el almacenamiento de agua total. Para el análisis de las precipitaciones se utilizaron grillas globales CMAP, encontrando que las mayores diferencias respecto a valores medios se producen entre los meses de diciembre de 2015 y marzo de 2016, en donde se observa una caída de hasta un 60% de las precipitaciones respecto a los valores esperados en la región norte del continente Sudamericano. A partir de la información provista por la misión satelital GRACE, se evaluaron anomalías del almacenamiento hídrico, obteniéndose disminuciones de hasta 60 cm en el norte y aumentos de 40 cm en el sur de Brasil respectivamente durante el evento El Niño 2015-2016. Finalmente, se investigó el efecto sobre la componente vertical de las coordenadas distinguiendo incrementos de la misma durante el evento 2015-2016 en la región norte de Sudamérica mientras, que en la región ecuatorial sur, se detectó un marcado efecto opuesto.El Niño-Southern Oscillation (ENSO) is an atmospheric-oceanic phenomenon that originates in the equatorial Pacific Ocean. It is characterized by two phases: the warm or “El Niño” phase, and the cold or “La Niña” phase. They respectively refer to a significant increase or decrease of the surface temperature of the Pacific Ocean with respect to normal values.One of the main consequences of this abnormality is an alteration of the hydrological cycle in the rainfall patterns in South American and Caribbean region. Such disturbance can cause non-periodic variations in both the rainfall patterns and water body storages located on the surface or near it. The immediate consequence is the pressure that such bodies exert on the earth's crust change. They can cause geometric movements of the earth's crust and gravity measurement changes.This paper is focused on the geometric effects of this phenomenon on the GNSS station positions of SIRGAS-CON network. Time periods for whichEl Niño or La Niña occurred are recognized using the Oceanic Niño Index (ONI). The impact of the most significant events, occurred between 2008-2012 and 2015-2016, over rainfall patterns and on total water storage is analyzed. Regions of characteristic behaviour of each phase are recognized using global precipitation model CMAP. The greatest differences with respect to average values occur between December 2015 and March 2016. A decrease up to 60% in rainfall is observed in the northern region of the South American continent. In order to evaluate water storage anomalies GRACE satellite mission data is assessed. A decrease up to 60 cm in Brazil northern region and an increase up to 40 cm in the southern region is observed during 2015-2016 El Niño event. Furthermore, the effect on the vertical component of the coordinates is investigated. Positive anomalies are found in the northern region of South America during the 2015-2016 event, while a significant opposite effect is detected in the southern equatorial region.Facultad de Ciencias Astronómicas y Geofísica

Impact of the extreme 2015-2016 Enos event on the geometry of the earth surface in the equatorial region of South America

El fenómeno del Niño-Oscilación del Sur (ENOS) es un fenómeno oceánico-atmosférico que se origina en las aguas ecuatoriales del Océano Pacífico. Existen dos fases, la fase cálida o El Niño y la fase fría o La Niña, y se refieren respectivamente a un aumento o disminución considerable de la temperatura superficial del océano respecto de los valores normales. Una de las consecuencias de esta alteración es un impacto en el ciclo hidrológico de la región de Sudamérica y el Caribe. Dicho fenómeno provoca variaciones no periódicas tanto en los patrones de precipitaciones como en el almacenamiento de las masas hídricas, que se sitúan sobre la superficie o en regiones cercanas a ella. La consecuencia inmediata son cambios en la presión que dichas masas ejercen sobre la corteza terrestre, los que provocan movimientos geométricos de la corteza y cambios en las medidas de gravedad. El objetivo del presente trabajo es analizar el efecto geométrico que dicho fenómeno tiene sobre la posición de las estaciones GNSS que integran la red SIRGAS-CON. En este estudio se reconocen los períodos temporales en donde se produjeron fenómenos de El Niño o La Niña por medio del Índice Oceánico El Niño (ONI), y se analiza el impacto de los eventos más significativos, ocurridos en 2008-2012 y 2015-2016, sobre los patrones de precipitación y sobre el almacenamiento de agua total. Para el análisis de las precipitaciones se utilizaron grillas globales CMAP, encontrando que las mayores diferencias respecto a valores medios se producen entre los meses de diciembre de 2015 y marzo de 2016, en donde se observa una caída de hasta un 60% de las precipitaciones respecto a los valores esperados en la región norte del continente Sudamericano. A partir de la información provista por la misión satelital GRACE, se evaluaron anomalías del almacenamiento hídrico, obteniéndose disminuciones de hasta 60 cm en el norte y aumentos de 40 cm en el sur de Brasil respectivamente durante el evento El Niño 2015-2016. Finalmente, se investigó el efecto sobre la componente vertical de las coordenadas distinguiendo incrementos de la misma durante el evento 2015-2016 en la región norte de Sudamérica mientras, que en la región ecuatorial sur, se detectó un marcado efecto opuesto.El Niño-Southern Oscillation (ENSO) is an atmospheric-oceanic phenomenon that originates in the equatorial Pacific Ocean. It is characterized by two phases: the warm or “El Niño” phase, and the cold or “La Niña” phase. They respectively refer to a significant increase or decrease of the surface temperature of the Pacific Ocean with respect to normal values.One of the main consequences of this abnormality is an alteration of the hydrological cycle in the rainfall patterns in South American and Caribbean region. Such disturbance can cause non-periodic variations in both the rainfall patterns and water body storages located on the surface or near it. The immediate consequence is the pressure that such bodies exert on the earth's crust change. They can cause geometric movements of the earth's crust and gravity measurement changes.This paper is focused on the geometric effects of this phenomenon on the GNSS station positions of SIRGAS-CON network. Time periods for whichEl Niño or La Niña occurred are recognized using the Oceanic Niño Index (ONI). The impact of the most significant events, occurred between 2008-2012 and 2015-2016, over rainfall patterns and on total water storage is analyzed. Regions of characteristic behaviour of each phase are recognized using global precipitation model CMAP. The greatest differences with respect to average values occur between December 2015 and March 2016. A decrease up to 60% in rainfall is observed in the northern region of the South American continent. In order to evaluate water storage anomalies GRACE satellite mission data is assessed. A decrease up to 60 cm in Brazil northern region and an increase up to 40 cm in the southern region is observed during 2015-2016 El Niño event. Furthermore, the effect on the vertical component of the coordinates is investigated. Positive anomalies are found in the northern region of South America during the 2015-2016 event, while a significant opposite effect is detected in the southern equatorial region.Fil: Galván, Romina de Los Angeles. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Carbonetti, Micaela Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Georreferenciación Satelitaria; ArgentinaFil: Gende, Mauricio Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Departamento de Georreferenciación Satelitaria; ArgentinaFil: Brunini, Claudio Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Laboratorio Geo - Aggo. Observatorio Geodésico Argentino Alemán; Argentin

Influence of production system and finishing feeding on meat quality of Rubia Gallega calves

Aim of study: Beef quality is mainly affected by finishing feeding (FF) and production system (PS). The effects of PS (extensive, semi-extensive, traditional and intensive systems) and FF from Rubia Gallega calves were compared in terms of meat quality.Area of study: Galicia (NW Spain)Material and methods: Calves (n=10 per treatment) were slaughtered at nine months of age and meat samples were assessed in terms of meat quality attributes such as physicochemical, nutritional and sensory analysis performed by a trained panel.Main results: Meat chemical composition varied (p<0.01) with PS and FF. The semi-extensive system showed the lowest values (p<0.05) for cooking loss (22.8%) and for shear force (26.0 N) while the extensive system presented the lowest contents of saturated fatty acids (SFA) and the highest contents of linolenic acid (p<0.001). The SFA and polyunsaturated fatty acid (PUFA) contents varied with FF (p<0.05). The lowest and highest values for SFA and PUFA were displayed in extensive group finished with Pasture/Concentrate, meanwhile feedlot group finished with Concentrate/Straw showed and opposite trend. The n-6/n-3 ratio was lower than 4 for extensive and semi-extensive systems (p<0.001). In addition, tenderness and juiciness showed significant differences mainly due to FF.Research highlights: This study showed that meat of calves reared in extensive systems was the healthiest, regarding total fat and fatty acid composition. It can be concluded that finishing feeding, and PS affected meat quality. Hence the potential usefulness of these results is to improve meat quality and safety according to market demands